linux-kernel - Re: v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb

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Date:   Wed, 25 Oct 2017 12:01:35 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     Wei Wei <dotweiba@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb_clone()

On Wed, Oct 25, 2017 at 11:49 AM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:

> From skb->dev and netdev_priv, the tun device has flags 0x1002 ==
> IFF_TAP | IFF_NO_PI. This kernel precedes the recent support for
> IFF_NAPI and IFF_NAPI_FRAGS. The allocation most likely happened
> in tun_build_skb from current->task_frag. It would be a previous
> allocation that left alloc_frag->offset unaligned. But perhaps this code
> needs to perform alignment before setting skb->head. At least on
> platforms where atomic on dataref must be aligned.

+1

Bug added in commit 66ccbc9c87c2 ("tap: use build_skb() for small packet")